Techniques for ghosting mitigation in coherent lidar systems using in-phase/quadrature phase (iq) processing

ABSTRACT

A light detection and ranging (LIDAR) system to transmit optical beams including at least up-chirp frequency and at least one down-chirp frequency toward targets in a field of view of the LIDAR system and receive returned signals of the up-chirp and the down-chirp as reflected from the targets. The LIDAR system may perform IQ processing on one or more returned signals to generate baseband signals in the frequency domain of the returned signals during the at least one up-chirp and the at least one down-chirp. The baseband signal includes a first set of peaks associated with the at least one up-chirp frequency and a second set of peaks associated with the at least one down-chirp frequency. The LIDAR system determines the target location using the first set of peaks and the second set of peaks.

RELATED APPLICATIONS

This application claims priority from and the benefit of U.S.Provisional Patent Application No. 63/165,601 filed on Mar. 24, 2021,the entire contents of which are incorporated herein by reference intheir entirety.

FIELD

The present disclosure is related to LIDAR (light detection and ranging)systems in general, and more particularly to ghosting mitigation incoherent LIDAR systems.

BACKGROUND

LIDAR systems, such as frequency-modulated continuous-wave (FMCW) LIDARsystems use tunable, infrared lasers for frequency-chirped illuminationof targets, and coherent receivers for detection of backscattered orreflected light from the targets that are combined with a local copy ofthe transmitted signal. Mixing the local copy with the return signal(e.g., a returned signal), delayed by the round-trip time to the targetand back, generates signals at the receiver with frequencies that areproportional to the distance to each target in the field of view of thesystem. An up sweep of frequency and a down sweep of frequency may beused to detect a range and velocity of a detected target. However, whenone or more of the LIDAR system and a target (or multiple targets) aremoving, the issue of associating the peaks corresponding to each targetarises.

SUMMARY

The present disclosure describes examples of systems and methods forghosting mitigation in coherent LIDAR systems.

According to one aspect, the present disclosure relates to a method. Themethod includes transmitting, toward a target in a field of view of alight detection and ranging (LIDAR) system, one or more optical beamsincluding at least one up-chirp frequency and at least one down-chirpfrequency. The method also includes receiving, from the target, a set ofreturned signals based on the one or more optical beams. The methodfurther includes determining whether peaks associated with the targetare within one or more sets of frequency ranges including signalattribute values corresponding to a lower likelihood of accuratelycalculating a location or speed of the target. The method furtherincludes, provided the peaks associated with the target are within theone or more sets of frequency ranges, performing in-phase quadraturephase (IQ) processing on the one or more received signals. The set ofreturned signals includes a Doppler shifted up-chirp frequency shiftedfrom the at least one up-chirp frequency caused by a relative motionbetween the target and the LIDAR system, and a Doppler shifteddown-chirp frequency shifted from the at least one down-chirp frequencycaused by the relative motion between the target and the LIDAR system.The Doppler shifted up-chirp frequency and the Doppler shifteddown-chirp frequency produce a first set of peaks associated with the atleast one up-chirp frequency corresponding to a target location of thetarget and a second set of peaks associated with the at least onedown-chirp frequency corresponding to the target location. The methodfurther includes, determining one or more of the target location, atarget velocity, and a target reflectivity using the first set of peaksand the second set of peaks.

In one embodiment, the first set of peaks includes a first true peak anda first image peak, the second set of peaks includes a second true peakand a second image peak, the IQ processing reduces a first magnitude ofthe first image peak and a second magnitude of the second image peak.

In one embodiment, determining the target location using the first setof peaks and the second set of peaks includes selecting the first truepeak from the first set of peaks and the second true peak from thesecond set of peaks and determining the target location based on thefirst true peak and the second true peak.

In one embodiment, the one or more sets of frequency ranges are based onan ego-velocity of the LIDAR system.

In one embodiment, performing IQ processing includes generating a firstsignal and second signal based on the set of returned signals, whereinthe first signal is shifted 90 degrees from the second signal,generating a third signal, wherein the third signal includes acombination of the first signal and an imaginary unit, and combining thethird and the second signal to generate a combined signal.

In one embodiment, performing IQ processing further includes applying afast Fourier transformer to the combined signal.

In one embodiment, combining the third and the second signal includessubtracting the third signal from the second signal for an up-chirp andadding the third signal to the second signal for a down-chirp, or addingthe third signal to the second signal for an up-chirp and subtractingthe third signal from the second signal for a down-chirp.

In one embodiment, subtracting the third signal from the second signalfor an up-chirp and adding the third signal to the second signal for adown-chirp reduces a range of frequencies that is processed to determineone or more of the target location, the target velocity, and the targetreflectivity.

In one embodiment, the method further includes, provided the peaksassociated with the target are not within the one or more sets offrequency ranges, refraining from using in-phase quadrature phase (IQ)circuitry.

According to one aspect, the present disclosure relates to a lightdetection and ranging (LIDAR) system. The LIDAR system includes anoptical scanner to transmit one or more optical beams including at leastone up-chirp frequency and at least one down-chirp frequency toward atargets in a field of view of the LIDAR system and receive a set ofreturned signals based on the one or more optical beams. The LIDARsystem also includes an optical processing system coupled to the opticalscanner to generate a baseband signal in a time domain from the returnsignal, the baseband signal including frequencies corresponding to LIDARtarget ranges. The LIDAR system further includes a signal processingsystem coupled to the optical processing system. The signal processingsystem includes a processing device and a memory to store instructionsthat, when executed by the processing device, cause the LIDAR system todetermine whether peaks associated with the target are within one ormore sets of frequency ranges including signal attribute valuescorresponding to a lower likelihood of accurately calculating a locationor speed of the target, provided the peaks associated with the targetare within the one or more sets of frequency ranges, perform in-phasequadrature phase (IQ) processing on the one or more received signalswherein, the set of returned signals includes a Doppler shifted up-chirpfrequency shifted from the at least one up-chirp frequency caused by arelative motion between the target and the LIDAR system, and a Dopplershifted down-chirp frequency shifted from the at least one down-chirpfrequency caused by the relative motion between the target and the LIDARsystem, and the Doppler shifted up-chirp frequency and the Dopplershifted down-chirp frequency produce a first set of peaks associatedwith the at least one up-chirp frequency corresponding to a targetlocation of the target and a second set of peaks associated with the atleast one down-chirp frequency corresponding to the target location, anddetermine one or more of the target location, a target velocity, and atarget reflectivity using the first set of peaks and the second set ofpeaks.

In one embodiment, the first set of peaks includes a first true peak anda first image peak, the second set of peaks includes a second true peakand a second image peak, and the IQ processing reduces a first magnitudeof the first image peak and a second magnitude of the second image peak.

In one embodiment, to determine the target location using the first setof peaks and the second set of peaks the LIDAR system is further toselect the first true peak from the first set of peaks and the secondtrue peak from the second set of peaks, and determine the targetlocation based on the first true peak and the second true peak.

In one embodiment, the one or more sets of frequency ranges are variablebased on an ego-velocity of the LIDAR system.

In one embodiment, to perform IQ processing the LIDAR system is furtherto: generate first signal and a second signal based on the set ofreturned signals, wherein the first signal is shifted 90 degrees fromthe second signal, generate a third signal, wherein the third signalincludes a combination of the first signal and an imaginary unit, andcombine the third and the second signal to generate a combined signal.

In one embodiment, to perform IQ processing the LIDAR system is furtherto apply a fast Fourier transformer to the combined signal.

In one embodiment, to combine the third signal and the second signal theLIDAR system is further to subtract the third signal from the secondsignal for an up-chirp and add the j third signal to the second signalfor a down-chirp, or add the third signal to the second signal for anup-chirp and subtract the third signal from the second signal for adown-chirp.

In one embodiment, subtracting the third signal from the second signalfor an up-chirp and adding the third signal to the second signal for adown-chirp reduces a range of frequencies that is processed to determineone or more of the target location, the target velocity, and the targetreflectivity.

In one embodiment, the LIDAR system is further to, provided the peaksassociated with the target are not within the one or more sets offrequency ranges, refrain from using in-phase quadrature phase (IQ)circuitry.

According to one aspect, the present disclosure relates to a lightdetection and ranging (LIDAR) system. The LIDAR system includes aprocessor, and a memory to store instructions that, when executed by theprocessor, cause the LIDAR system to: transmit, toward a target in afield of view of the LIDAR system, one or more optical beams includingat least one up-chirp frequency and at least one down-chirp frequency;receive, from the target, a set of returned signals based on the one ormore optical beams; determine whether peaks associated with the targetare within one or more sets of frequency ranges including signalattribute values corresponding to a lower likelihood of accuratelycalculating a location or speed of the target; provided the peaksassociated with the target are within the one or more sets of frequencyranges, perform in-phase quadrature phase (IQ) processing on the one ormore received signals wherein, the set of returned signals includes aDoppler shifted up-chirp frequency shifted from the at least oneup-chirp frequency caused by a relative motion between the target andthe LIDAR system, and a Doppler shifted down-chirp frequency shiftedfrom the at least one down-chirp frequency caused by the relative motionbetween the target and the LIDAR system, and the Doppler shiftedup-chirp frequency and the Doppler shifted down-chirp frequency producea first set of peaks associated with the at least one up-chirp frequencycorresponding to a target location of the target and a second set ofpeaks associated with the at least one down-chirp frequencycorresponding to the target location, and determine one or more of thetarget location, a target velocity, and a target reflectivity using thefirst set of peaks and the second set of peaks.

In one embodiment, the first set of peaks includes a first true peak anda first image peak, the second set of peaks includes a second true peakand a second image peak, and the IQ processing reduces a first magnitudeof the first image peak and a second magnitude of the second image peak.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of various examples, reference is nowmade to the following detailed description taken in connection with theaccompanying drawings in which like identifiers correspond to likeelements.

FIG. 1 is a block diagram illustrating an example LIDAR system accordingto the present disclosure.

FIG. 2 is a time-frequency diagram illustrating one example of LIDARwaveforms according to the present disclosure.

FIG. 3A is a block diagram illustrating an example LIDAR systemaccording to the present disclosure.

FIG. 3B is a block diagram illustrating an electro-optical opticalsystem according to the present disclosure.

FIG. 4 is a block diagram of an example signal processing systemaccording to the present disclosure.

FIG. 5 is a signal magnitude-frequency diagram illustrating signal peaksfor a target according to the present disclosure.

FIG. 6 is a block diagram of an example signal processing system forselecting peaks according to the present disclosure.

FIG. 7A is a magnitude-frequency diagram illustrating frequency rangesaccording to the present disclosure.

FIG. 7B is a magnitude-frequency diagram illustrating frequency rangesaccording to the present disclosure.

FIG. 8 is a flowchart illustrating a method for selecting peaksaccording to the present disclosure.

DETAILED DESCRIPTION

The present disclosure describes various examples of LIDAR systems andmethods for automatically mitigating ghosting that may occur due toDoppler shifts. According to some embodiments, the described LIDARsystem may be implemented in any sensing market, such as, but notlimited to, transportation, manufacturing, metrology, medical, virtualreality, augmented reality, and security systems. According to someembodiments, the described LIDAR system is implemented as part of afront-end of frequency modulated continuous-wave (FMCW) device thatassists with spatial awareness for automated driver assist systems, orself-driving vehicles.

LIDAR systems described by the embodiments herein include coherent scantechnology to detect a signal returned from a target to generate acoherent heterodyne signal, from which range and velocity information ofthe target may be extracted. A signal, or multiple signals, may includean up-sweep of frequency (up-chirp) and a down-sweep of frequency(down-chirp), either from a single optical source or from separateoptical source (i.e., one source with an up-sweep and one source with adown-sweep). Accordingly, two different frequency peaks, one for theup-chirp and one for the down-chirp, may be associated with a target andcan be used to determine target range and velocity. However, peak imagesmay also occur when the LIDAR system processes the signals. Peak imagesmay include data (e.g., graphical data) that includes signal attributes(e.g., SNR value) that suggests a weak correspondence between a detectedpeak and the location and/or speed of a target. Hence, if these peakimages are used by a LIDAR system to detect a target, the LIDAR systemwill use faulty data to process location, speed, velocity related to thetarget. Use of peak images in this fashion may be referred to as“ghosting.” Using the techniques described herein, embodiments of thepresent invention can, among other things, address the issues describedabove by introducing phase modulations into the sweeps/chirps. Thisallows the LIDAR system to match the peaks and/or peak images with anexpected peak shape to differentiate between the peaks (e.g., truepeaks) and peak images. In contrast to image peaks, true peaks includedata (e.g., graphical data) that includes signal attributes (e.g., a SNRvalue) that strongly corresponds to the location and/or speed of atarget. Hence, such peaks enable LIDAR systems to reliably identifylocations, speeds, velocities of a target. It should be noted that apeak image may also be referred to as an image peak.

FIG. 1 illustrates a LIDAR system 100 according to exampleimplementations of the present disclosure. The LIDAR system 100 includesone or more of each of a number of components, but may include fewer oradditional components than shown in FIG. 1. As shown, the LIDAR system100 includes optical circuits 101 implemented on a photonics chip. Theoptical circuits 101 may include a combination of active opticalcomponents and passive optical components. Active optical components maygenerate, amplify, and/or detect optical signals and the like. In someexamples, the active optical components include optical beams atdifferent wavelengths, and include one or more optical amplifiers, oneor more optical detectors, or the like.

Free space optics 115 may include one or more optical waveguides tocarry optical signals, and route and manipulate optical signals toappropriate input/output ports of the active optical components. Thefree space optics 115 may also include one or more optical componentssuch as taps, wavelength division multiplexers (WDM),splitters/combiners, polarization beam splitters (PBS), collimators,couplers or the like. In some examples, the free space optics 115 mayinclude components to transform the polarization state and directreceived polarized light to optical detectors using a PBS, for example.The free space optics 115 may further include a diffractive element todeflect optical beams having different frequencies at different anglesalong an axis (e.g., a fast-axis).

In some examples, the LIDAR system 100 includes an optical scanner 102that includes one or more scanning mirrors that are rotatable along anaxis (e.g., a slow-axis) that is orthogonal or substantially orthogonalto the fast-axis of the diffractive element to steer optical signals toscan an environment according to a scanning pattern. For instance, thescanning mirrors may be rotatable by one or more galvanometers. Theoptical scanner 102 also collects light incident upon any objects in theenvironment into a return optical beam that is returned to the passiveoptical circuit component of the optical circuits 101. For example, thereturn optical beam may be directed to an optical detector by apolarization beam splitter. In addition to the mirrors andgalvanometers, the optical scanner 102 may include components such as aquarter-wave plate, lens, anti-reflective coated window or the like.

To control and support the optical circuits 101 and optical scanner 102,the LIDAR system 100 includes LIDAR control systems 110. The LIDARcontrol systems 110 may include a processing device for the LIDAR system100. In some examples, the processing device may be one or moregeneral-purpose processing devices such as a microprocessor, centralprocessing unit, or the like. More particularly, the processing devicemay be complex instruction set computing (CISC) microprocessor, reducedinstruction set computer (RISC) microprocessor, very long instructionword (VLIW) microprocessor, or processor implementing other instructionsets, or processors implementing a combination of instruction sets. Theprocessing device may also be one or more special-purpose processingdevices such as an application specific integrated circuit (ASIC), afield programmable gate array (FPGA), a digital signal processor (DSP),network processor, or the like. In some examples, the LIDAR controlsystems 110 may include memory to store data, and instructions to beexecuted by the processing device. The memory may be, for example,read-only memory (ROM), random-access memory (RAM, programmableread-only memory (PROM), erasable programmable read-only memory (EPROM),electrically erasable programmable read-only memory (EEPROM), flashmemory, magnetic disk memory such hard disk drives (HDD), optical diskmemory such as compact-disk read-only (CD-ROM) and compact diskread-write memory (CD-RW), or any other type of non-transitory memory.

In some examples, the LIDAR control systems 110 may include a signalprocessing unit 112 such as a DSP. The LIDAR control systems 110 areconfigured to output digital control signals to control optical drivers103. In some examples, the digital control signals may be converted toanalog signals through signal conversion unit 106. For example, thesignal conversion unit 106 may include a digital-to-analog converter.The optical drivers 103 may then provide drive signals to active opticalcomponents of optical circuits 101 to drive optical sources such aslasers and amplifiers. In some examples, several optical drivers 103 andsignal conversion units 106 may be provided to drive multiple opticalsources.

The LIDAR control systems 110 are also configured to output digitalcontrol signals for the optical scanner 102. A motion control system 105may control the galvanometers of the optical scanner 102 based oncontrol signals received from the LIDAR control systems 110. Forexample, a digital-to-analog converter may convert coordinate routinginformation from the LIDAR control systems 110 to signals interpretableby the galvanometers in the optical scanner 102. In some examples, amotion control system 105 may also return information to the LIDARcontrol systems 110 about the position or operation of components of theoptical scanner 102. For example, an analog-to-digital converter may inturn convert information about the galvanometers' position to a signalinterpretable by the LIDAR control systems 110.

The LIDAR control systems 110 are further configured to analyze incomingdigital signals. In this regard, the LIDAR system 100 includes opticalreceivers 104 to measure one or more beams received by optical circuits101. For example, a reference beam receiver may measure the amplitude ofa reference beam from the active optical component, and ananalog-to-digital converter converts signals from the reference receiverto signals interpretable by the LIDAR control systems 110. Targetreceivers measure the optical signal that carries information about therange and velocity of a target in the form of a beat frequency,modulated optical signal. The reflected beam may be mixed with a secondsignal from a local oscillator. The optical receivers 104 may include ahigh-speed analog-to-digital converter to convert signals from thetarget receiver to signals interpretable by the LIDAR control systems110. In some examples, the signals from the optical receivers 104 may besubject to signal conditioning by signal conditioning unit 107 prior toreceipt by the LIDAR control systems 110. For example, the signals fromthe optical receivers 104 may be provided to an operational amplifierfor amplification of the received signals and the amplified signals maybe provided to the LIDAR control systems 110.

In some applications, the LIDAR system 100 may additionally include oneor more imaging devices 108 configured to capture images of theenvironment, a global positioning system 109 configured to provide ageographic location of the system, or other sensor inputs. The LIDARsystem 100 may also include an image processing system 114. The imageprocessing system 114 can be configured to receive the images andgeographic location, and send the images and location or informationrelated thereto to the LIDAR control systems 110 or other systemsconnected to the LIDAR system 100.

In operation according to some examples, the LIDAR system 100 isconfigured to use nondegenerate optical sources to simultaneouslymeasure range and velocity across two dimensions. This capability allowsfor real-time, long range measurements of range, velocity, azimuth, andelevation of the surrounding environment.

In some examples, the scanning process begins with the optical drivers103 and LIDAR control systems 110. The LIDAR control systems 110instruct the optical drivers 103 to independently modulate one or moreoptical beams, and these modulated signals propagate through the passiveoptical circuit to the collimator. The collimator directs the light atthe optical scanning system that scans the environment over apreprogrammed pattern defined by the motion control system 105. Theoptical circuits 101 may also include a polarization wave plate (PWP) totransform the polarization of the light as it leaves the opticalcircuits 101. In some examples, the polarization wave plate may be aquarter-wave plate or a half-wave plate. A portion of the polarizedlight may also be reflected back to the optical circuits 101. Forexample, lensing or collimating systems used in LIDAR system 100 mayhave natural reflective properties or a reflective coating to reflect aportion of the light back to the optical circuits 101.

Optical signals reflected back from the environment pass through theoptical circuits 101 to the receivers. Because the polarization of thelight has been transformed, it may be reflected by a polarization beamsplitter along with the portion of polarized light that was reflectedback to the optical circuits 101. Accordingly, rather than returning tothe same fiber or waveguide as an optical source, the reflected light isreflected to separate optical receivers. These signals interfere withone another and generate a combined signal. Each beam signal thatreturns from the target produces a time-shifted waveform. The temporalphase difference between the two waveforms generates a beat frequencymeasured on the optical receivers (photodetectors). The combined signalcan then be reflected to the optical receivers 104.

The analog signals from the optical receivers 104 are converted todigital signals using ADCs. The digital signals are then sent to theLIDAR control systems 110. A signal processing unit 112 may then receivethe digital signals and interpret them. In some embodiments, the signalprocessing unit 112 also receives position data from the motion controlsystem 105 and galvanometers (not shown) as well as image data from theimage processing system 114. The signal processing unit 112 can thengenerate a 3D point cloud with information about range and velocity ofpoints in the environment as the optical scanner 102 scans additionalpoints. The signal processing unit 112 can also overlay a 3D point clouddata with the image data to determine velocity and distance of objectsin the surrounding area. The system also processes the satellite-basednavigation location data to provide a precise global location.

FIG. 2 is a time-frequency diagram 200 of a scanning signal 201 that canbe used by a LIDAR system, such as system 100, to scan a targetenvironment according to some embodiments. In one example, the scanningwaveform 201, labeled as f_(FM)(t), is a sawtooth waveform (sawtooth“chirp”) with a chirp bandwidth Δf_(C) and a chirp period T_(C). Theslope of the sawtooth is given as k=(Δf_(C)/T_(C)). FIG. 2 also depictstarget return signal 202 (e.g., a returned signal) according to someembodiments. Target return signal 202, labeled as f_(FM)(t−Δt), is atime-delayed version of the scanning signal 201, where Δt is the roundtrip time to and from a target illuminated by scanning signal 201. Theround trip time is given as Δt=2R/v, where R is the target range and vis the velocity of the optical beam, which is the speed of light c. Thetarget range, R, can therefore be calculated as R=c(Δt/2). When thereturn signal 202 is optically mixed with the scanning signal, a rangedependent difference frequency (“beat frequency”) Δf_(R)(t) isgenerated. The beat frequency Δf_(R)(t) is linearly related to the timedelay Δt by the slope of the sawtooth k. That is, Δf_(R)(t)=kΔt. Sincethe target range R is proportional to Δt, the target range R can becalculated as R=(c/2)(Δf_(R)(t)/k). That is, the range R is linearlyrelated to the beat frequency Δf_(R)(t). The beat frequency Δf_(R)(t)can be generated, for example, as an analog signal in optical receivers104 of system 100. The beat frequency can then be digitized by ananalog-to-digital converter (ADC), for example, in a signal conditioningunit such as signal conditioning unit 107 in LIDAR system 100. Thedigitized beat frequency signal can then be digitally processed, forexample, in a signal processing unit, such as signal processing unit 112in system 100. It should be noted that the target return signal 202will, in general, also includes a frequency offset (Doppler shift) ifthe target has a velocity relative to the LIDAR system 100. The Dopplershift can be determined separately, and used to correct the frequency ofthe return signal, so the Doppler shift is not shown in FIG. 2 forsimplicity and ease of explanation. It should also be noted that thesampling frequency of the ADC will determine the highest beat frequencythat can be processed by the system without aliasing. In general, thehighest frequency that can be processed is one-half of the samplingfrequency (i.e., the “Nyquist limit”). In one example, and withoutlimitation, if the sampling frequency of the ADC is 1 gigahertz, thenthe highest beat frequency that can be processed without aliasing(Δf_(R max)) is 500 megahertz. This limit in turn determines the maximumrange of the system as R_(max)=(c/2)(Δf_(R max)/k) which can be adjustedby changing the chirp slope k. In one example, while the data samplesfrom the ADC may be continuous, the subsequent digital processingdescribed below may be partitioned into “time segments” that can beassociated with some periodicity in the LIDAR system 100. In oneexample, and without limitation, a time segment might correspond to apredetermined number of chirp periods T, or a number of full rotationsin azimuth by the optical scanner.

FIG. 3A is a block diagram illustrating an example LIDAR system 300according to the present disclosure. In one example system 300 includesan optical scanner 301 to transmit an optical beam, such as a FMCW(frequency-modulated continuous wave) infrared (IR) optical beam 304 andto receive a return signal 313 from reflections of the optical beam 304from targets such as target 312 in the field of view (FOV) of theoptical scanner 301. System 300 also includes an optical processingsystem 302 to generate a baseband signal 314 in the time domain from thereturn signal 313, where the baseband signal 314 contains frequenciescorresponding to LIDAR target ranges. Optical processing system 302 mayinclude elements of free space optics 115, optical circuits 101, opticaldrivers 103 and optical receivers 104 in LIDAR system 100. System 300also includes a signal processing system 303 to measure energy of thebaseband signal 314 in the frequency domain, to compare the energy to anestimate of LIDAR system noise, and to determine a likelihood that asignal peak in the frequency domain indicates a detected target. Signalprocessing system 303 may include elements of signal conversion unit106, signal conditioning unit 107, LIDAR control systems 110 and signalprocessing unit 112 in LIDAR system 100.

FIG. 3B is a block diagram illustrating an example electro-opticalsystem 350. Electro-optical system 350 includes the optical scanner 301,similar to the optical scanner 102 illustrated and described in relationto FIG. 1. Electro-optical system 350 also includes the opticalprocessing system 302, which as noted above, may include elements offree space optics 115, optical circuits 101, optical drivers 103, andoptical receivers 104 in LIDAR system 100.

Electro-optical processing system 302 includes an optical source 305 togenerate the optical beam 304. The optical beam 304 may be directed toan optical coupler 306 that is configured to couple the optical beam 304to a polarization beam splitter (PBS) 307 and a sample 308 of theoptical beam 304 to a photodetector (PD) 309. The PBS 307 is configuredto direct the optical beam 304, because of its polarization, toward theoptical scanner 301. Optical scanner 301 is configured to scan a targetenvironment with the optical beam 304, through a range of azimuth andelevation angles covering the field of view (FOV) 310 of a LIDAR window311 in an enclosure 320 of the optical system 350. In FIG. 3B, for easeof illustration, only the azimuth scan is illustrated.

As shown in FIG. 3B, at one azimuth angle (or range of angles), theoptical beam 304 passes through the LIDAR window 311 and illuminates atarget 312. A return signal 313 from the target 312 passes through LIDARwindow 311 and is directed by optical scanner 301 back to the PBS 307.

The return signal 313, which will have a different polarization than theoptical beam 304 due to reflection from the target 312, is directed bythe PBS 307 to the photodetector (PD) 309. In PD 309, the return signal313 is optically mixed with the local sample 308 of the optical beam 304to generate a range-dependent baseband signal 314 in the time domain.The range-dependent baseband signal 314 is the frequency differencebetween the local sample 308 of the optical beam 304 and the returnsignal 313 versus time (i.e., Δf_(R)(t)). The range-dependent basebandsignal 314 may be in a frequency domain and may be generated by mixingat least one up-chirp frequency and at least one down-chirp frequencywith the return signal 313. The at least one down-chirp frequency may bedelayed in time proportional to the relative motion of at least one ofthe target and the LIDAR system.

FIG. 4 is a detailed block diagram illustrating an example of the signalprocessing system 303, which processes the baseband signal 314 accordingto some embodiments. As noted above, signal processing unit 303 mayinclude elements of signal conversion unit 106, signal conditioning unit107, LIDAR control systems 110 and signal processing unit 112 in LIDARsystem 100.

Signal processing system 303 includes an analog-to-digital converter(ADC) 401, a time domain signal processor 402, a block sampler 403, adiscrete Fourier transform processor 404, a frequency domain signalprocessor 405, and a peak search processor 406. The component blocks ofsignal processing system 303 may be implemented in hardware, firmware,software, or some combination of hardware, firmware and software.

In FIG. 4, the baseband signal 314, which is a continuous analog signalin the time domain, is sampled by ADC 401 to generate a series of timedomain samples 315. The time domain samples 315 are processed by thetime domain processor 402, which conditions the time domain samples 315for further processing. For example, time domain processor 402 may applyweighting or filtering to remove unwanted signal artifacts or to renderthe signal more tractable for subsequent processing. The output 316 oftime domain processor 402 is provided to block sampler 403. Blocksampler 403 groups the time domain samples 316 into groups of N samples317 (where N is an integer greater than 1), which are provided to DFTprocessor 404. DFT processor 404 transforms the groups of N time domainsamples 317 into N frequency bins or subbands 318 in the frequencydomain, covering the bandwidth of the baseband signal 314. The Nsubbands 319 are provided to frequency domain processor 405, whichconditions the subbands for further processing. For example, frequencydomain processor 405 may resample and/or average the subbands 319 fornoise reduction. Frequency domain processor 405 may also calculatesignal statistics and system noise statistics. The processed subbands319 are then provided to a peak search processor 406 that searches forsignal peaks representing detected targets in the FOV of the LIDARsystem 300.

FIG. 5 is an example of a signal magnitude-frequency diagram 500illustrating signal peaks for one or more targets according to someembodiments. An LIDAR system (e.g., a FMCW LIDAR system) may generate anup-chirp and a down-chirp frequency modulation (also referred to hereinas up-sweep and down-sweep) to scan an environment and to determinerange and velocity of one or more targets within that environment. Inone example, a single optical source may generate both the up-chirp andthe down-chirp. In another example, the system may include an opticalsource to generate a signal that includes the up-chirp and anotheroptical source to generate a signal that includes the down-chirp. Usingthe returned signal and corresponding generated beat frequencies (i.e.,peak frequencies) from the up-chirp and down-chirp, a signal processingsystem can determine one or more of a range of a target and a velocityof the target. For instance, according to some embodiments, the signalprocessing unit 112 can be configured to determine the range of thetarget by calculating a distance from the LIDAR system 500 usingmultiple frequencies corresponding to respective peaks. As discussedabove, the signal processing unit 112 may generate a baseband signal ina frequency domain by mixing at least one up-chirp frequency and atleast one down-chirp frequency with the one or more returned signals.The at least one down-chirp frequency may be delayed in timeproportional to the relative motion of at least one of the target andthe LIDAR system 500. The baseband signal may include the peaks 505A,505B, 510A, and 510B, and may include additional peaks (not illustratedin FIG. 5).

According to some embodiments, the signal processing unit 112 can beconfigured to determine the velocity of the target using differencesbetween the multiple frequencies corresponding to the peaks. However, asdepicted in FIG. 5, there may arise situations in which image peaks(sometimes referred to as “mirror images,” “image ghosts” or the like)are also present in the baseband signal. This may cause the LIDAR systemto detect false (or “fake”) targets rather than desirable “true” targetsor peaks (or “true images” or “true peaks”).

As illustrated in FIG. 5, the signal magnitude-frequency diagram 500includes peak 505A, peak 505B, peak 510A, and peak 510B. A frequency of0 (e.g., 0 hertz, 0 terahertz, etc.) is also indicated in the signalmagnitude-frequency diagram 500. Peaks 505A, 505B, 510A and 510B may bepresent in the baseband signal that is processed and/or analyzed by asignal processing unit of the LIDAR system (e.g., signal processing unit112 illustrated in FIG. 1), as discussed in more detail below. Peak 505Bmay be a mirror image of peak 505A. For example, peak 505B is mirroredacross the frequency 0 and shares the same properties of peak 505A(e.g., same curvature or shape). Peak 505B may be referred to as a peakimage or image peak. Peak 505A may be conjugate symmetric to peak 505Band vice versa. Peak 510B may be a mirror image of peak 510A. Forexample, peak 510B is mirrored across the frequency 0 and shares thesame properties of peak 510A (e.g., same curvature or shape). Peak 510Bmay also be referred to as a peak image or image peak. In somescenarios, peak 505A is shifted (e.g., moved) upwards in frequency fromthe location of the target. Peak 505A may be referred to as an upshiftedpeak, as a Doppler shifted peak, or as F_(up). Peak 510A is shifteddownwards in frequency from the location of the target (as indicated bythe solid vertical line in the signal magnitude-frequency diagram 500).Peak 510A may be referred to as a downshifted peak, as a Doppler shiftedpeak, or as F_(dn). The shift in the peaks may be due to, for example,the movement of one or more of the target and/or sensors from a LIDARsystem (e.g., a FMCW or similar LIDAR system). For example, the targetmay be moving, the device (e.g., a vehicle, a smartphone, etc.) thatincludes the LIDAR sensors (e.g., optical scanner 102 and/or opticalcircuits 101 illustrated in FIG. 1, etc.) may be moving, or both thetarget and the device may be moving relative to a particular point.

Because peak 505A has been shifted up (e.g., upshifted) to a higherfrequency, peak 505B (e.g., a peak image) is located at a correspondingnegative frequency. For example, if peak 505A was shifted to a frequencyJ, then peak 505B would be located at the frequency −J. In addition,because peak 510A has been shifted down (e.g., downshifted) to a lowerfrequency, peak 510B (e.g., a peak image) is located at a correspondingpositive frequency. Peak 505B may be referred to as −F_(up) and peak510B may be referred to as −F_(dn). In some embodiments, peak 505A (andcorresponding peak 505B) may correspond to the up-chirp signals (e.g.,up-chirp signals from a particular target), and 510A (and correspondingpeak 510B) may correspond to down-chirp signals. In other embodiments,peak 505A (and corresponding peak 505B) may correspond to the down-chirpsignals, and 510A (and corresponding peak 510B) may correspond to theup-chirp signals (e.g., down-chirp signals from a particular target).

In some embodiments, the LIDAR system (e.g., signal processing unit 112of LIDAR system 100 illustrated in FIG. 1) may be configured to selectpeak 505A. For instance, when the target is at a closer range (e.g.,within a first threshold range of the LIDAR), the peak with the highestfrequency (e.g., peak 505A) may be determined to be a true peakcorresponding to a target, rather than a peak image, and hence selectedby the LIDAR system (e.g., signal processing unit 112 illustrated inFIG. 1). In this fashion, the signal processing unit 112 is configuredto select peak 505A based on the type of ghosting that is occurring(e.g., close-range ghosting or far-range ghosting). Thus, the LIDAR(e.g., signal processing unit 112 illustrated in FIG. 1) may be able todetermine that the peak 505A should be selected for range and/ordistance determinations related to the target. In addition, because theLIDAR system (e.g., signal processing unit 112 illustrated in FIG. 1)has determined that the peak 505A is a true peak (and not a peak image),the LIDAR system may also determine that peak 505B (which has thenegative frequency of peak 505A) is a peak image. In some embodiments,the LIDAR system may be configured to discard peak 505B (e.g., discardpeak images).

As discussed above, there may arise situations in which peak images(e.g., peaks 505B and 510B) are also present. For example, due tohardware and computational resources, the beat signal may undergo realsampling and frequency peaks may be assumed to be positive. However, ifthe target is at a closer range (e.g., within a first threshold range ofthe LIDAR system), a negative Doppler shift can cause a beat frequencypeak to become negative. For example, due to downshifting, the peak 510Acan have a negative frequency. In contrast to embodiments of the presentdisclosure, this may cause conventional systems to select peak 510Binstead of peak 510A when determining the location of the target. Forexample, when peak 505A and peak 510A are used, the target location maybe determined as follows: (F_(up)−F_(dn))/2. Thus, the target (e.g., thetrue target location) would likely be determined to be towards themiddle of peak 505A and peak 510A (not depicted). However, if peak 505Aand peak 510B are used, the target location (e.g., the location of aghost or ghost target) may be determined as follows: (F_(up)+F_(dn))/2.

If there is no Doppler shift, the peaks in the baseband signal may be atpositive frequencies. However, due to Doppler shift, peaks correspondingto close range targets might shift to negative frequencies that areclose to 0 Hz and peaks corresponding to far range targets might shiftto negative frequencies that close to −((sampling frequency)/2). Thus,the LIDAR system should determine which peaks correspond to the truepeak and if a false peak is selected a ghosting may occur (e.g., a ghostimage may be detected by the LIDAR system). Without IQ processing, thepeak 505B may have the same height (e.g., magnitude) and shape as peak505C, and the peak 510B may have the same height (e.g., magnitude) andshape as peak 510C. If the peak 505B remains at the height/magnitude ofpeak 505C and the peak 510B remains at the height/magnitude of peak510C, this may cause the LIDAR system 100 to select the wrong peak(e.g., peak 505B and/or 510B) when determining the location, velocity,and/or reflectivity of the target.

In one embodiment, the LIDAR system (e.g., signal processing unit 112 ofLIDAR system 100 illustrated in FIG. 1) may perform in-phase quadraturephase (IQ) processing on the returned signals (e.g., received signals).The IQ processing of the returned signals may allow the LIDAR system toidentify true peaks within the baseband signal more easily, quickly,efficiently, etc., as discussed in more detail below.

In one embodiment, the LIDAR system (e.g., signal processing unit 112 ofLIDAR system 100 illustrated in FIG. 1) may perform IQ processing on thereturned signals by generating a quadrature signal and an in-phasesignal based on the returned signals. The quadrature signal may beshifted 90 degrees from the in-phase signal. The LIDAR system maygenerate the in-phase signal by downshifting a returned signal by thecorresponding transmitted signal (e.g., a local copy of the signal thatwas transmitted). For example, a mixing module may receive the returnedsignal and the corresponding transmitted signal, and may downshift thereturned signal by the corresponding transmitted signal. The LIDARsystem may generate the quadrature signal by downshifting the returnedsignal by a 90-degree phase shifted version of the correspondingtransmitted signal (e.g., by phase shifting the correspondingtransmitted signal by 90 degrees). For example, another mixing modulemay receive the returned signal and 90-degree phase shifted version ofthe corresponding transmitted signal, and may downshift the returnedsignal by the 90-degree phase shifted version of the correspondingtransmitted signal. The 90-degree phase shifted version of thecorresponding transmitted signal may be generated by a phase shiftingmodule, as discussed in more detail below.

In one embodiment, the LIDAR system (e.g., signal processing unit 112 ofLIDAR system 100 illustrated in FIG. 1) may add (e.g., combine, mix,etc.) the in-phase signal and the quadrature signal to generate acombined signal. The combined signal may also be referred to as a mixedsignal, an aggregate signal, a summed signal, etc. The LIDAR system mayalso perform a fast Fourier transform (FFT) on the combined signal to.For example, the combined signal may be provided to a FFT module whichmay apply a fast Fourier transform to the combined signal to generatethe frequency spectrum of the baseband signal.

In one embodiment, the combined signal may be a complex signal (e.g., asignal that includes a complex or imaginary component). Because thecombined signal is a complex signal, the fast Fourier transform of thecombined signals may no longer be symmetric. For example, prior to theIQ processing, the peak 505B (e.g., an image peak) may be an exactmirror image of the peak 505A (e.g., the peak 505B would be the samemagnitude/height as peak 505A). However, after IQ processing themagnitude/height of peak 505B may be reduced, suppressed, minimized,etc., when compared to the magnitude/height of peak 505A. In anotherexample, prior to the IQ processing, the peak 510B (e.g., an image peak)may be an exact mirror image of the peak 510A (e.g., the peak 510B wouldbe the same magnitude/height as peak 510A). However, after IQ processingthe magnitude/height of peak 510B may be reduced, suppressed, minimized,etc., when compared to the magnitude/height of peak 510A. The combinedsignals (e.g., complex signals) may be represented as I+(j*Q), where Iis the in-phase signal, Q is the quadrature signal, and j is animaginary unit.

In one embodiment, the LIDAR system (e.g., signal processing unit 112 ofLIDAR system 100 illustrated in FIG. 1) may combine (e.g., add) thein-phase signal and the quadrature signal by subtracting the quadraturesignal from the in-phase signal if the transmitted signal was anup-chirp. For example, if the corresponding transmitted signal (for areturned signal) had an up-sweep of frequency, the LIDAR system maycombine the in-phase signal and the quadrature signal by subtracting thesignal j*Q from the in-phase signal (or by adding a negative of thesignal j*Q to the in-phase signal).

In one embodiment, the LIDAR system (e.g., signal processing unit 112 ofLIDAR system 100 illustrated in FIG. 1) may combine the in-phase signaland the quadrature signal by adding the quadrature signal to thein-phase signal if the transmitted signal was a down-chirp. For example,if the corresponding transmitted signal (for a returned signal) had adown-sweep of frequency, the LIDAR system may add the in-phase signaland the quadrature signal multiplied by j to generate a complex signal.

In one embodiment, the LIDAR system (e.g., signal processing unit 112 ofLIDAR system 100 illustrated in FIG. 1) may determine one or more of atarget location (e.g., the location of the target), a target velocity(e.g., a velocity of the target), and a target reflectivity (e.g., thereflectivity of the target) using peaks 505A, 505B, 510A, and 510B. Forexample, after IQ processing, the magnitude/height of the peaks 505B and510B (e.g., the images peaks) may be reduced or suppressed. The LIDARsystem may use the peaks with the highest magnitude/height to determine(e.g., calculate) one or more of the location, velocity, andreflectivity of the target. For example, the LIDAR system may selectpeak 505A from the set of peaks (e.g., pair of peaks) that includes peak505A and 505B. The LIDAR system may also select peak 510A from the setof peaks (e.g., pair of peaks) that includes peak 510A and 510B. TheLIDAR system may determine the location, velocity, and reflectivity ofthe target based on peaks 505A and 510A.

In one embodiment, the LIDAR system (e.g., signal processing unit 112 ofLIDAR system 100 illustrated in FIG. 1) may subtract the signal j*Q fromthe in-phase signal for an up-chirp and add the quadrature signal to thein-phase signal for a down-chirp to reduce a range of frequencies thatis processed to determine one or more of the target location, the targetvelocity, and the target reflectivity. Without Doppler shift, the beatfrequency F_(peak) for a given chirp would be equal to the chirp rate(α), multiplied by the delay/time to the target and back to the LIDARsystem (τ). The beat frequency without Doppler shift may be representedas F_(peak)=α*τ. For an up-sweep, α would be positive, thus F_(peak)would be at positive frequencies and a corresponding image peak would beat negative frequencies. For a down-sweep, α would be negative thusF_(peak) would be at negative frequencies and a corresponding image peakwould be at positive frequencies. To reduce the range or amount offrequencies that are processed by the LIDAR system, the combined signalmay be determined (e.g., generated, computed, constructed, etc.) asI−(j*Q) for up-chirps and I+(j*Q) for down-chirps. This may cause all ofthe true peaks to be at positive frequencies in the absence of dopplershift. For example, this may cause the location of peak 510A to be at apositive frequency. This may allow the LIDAR system to process (e.g.,analyze, scan, etc.) a smaller range or amount of frequencies (e.g., thepositive frequencies) when identifying the true peaks (e.g., peaks 505Aand 510A). If there is Doppler shift, the beat frequency for a chirp maybe represented as F_(peak)=|α|*τ+D, where D is the Doppler shift. Thusone or more of the true peaks may be located at negative frequencies dueto the Doppler shift. However, for a specified maximum Doppler shiftD_(max), the true peak location may be limited to negative frequenciesin the range of −D_(max) to 0 or −F_(sample)/2 to −F_(sample)/2−D_(max).To reduce the range or amount of frequencies that are processed by theLIDAR system, the combined signal may be determined (e.g., generated,computed, constructed, etc.) as I+(j*Q) for up-chirps and I−(j*Q) fordown-chirps. This may cause all of the true peaks to be at negativefrequencies. With Doppler shift, the true peaks may be located atcertain positive frequencies. The LIDAR system is able to process asmaller range or amount of frequencies (e.g., the negative frequencies)when identifying the true peaks (e.g., peaks 505A and 510A).

In one embodiment, the LIDAR system (e.g., signal processing unit 112 ofLIDAR system 100 illustrated in FIG. 1) may determine whether the targetis within one or more sets of ranges where ghosting can occur. Forexample, referring to FIG. 7, the LIDAR system may determine whether anyof the peaks associated with the target is within a close ghosting range(e.g., a range of frequencies where close range ghosting may occur) or afar ghosting range (e.g., a range of frequencies where far rangeghosting may occur). The LIDAR system may use the true and image peaklocations to determine or estimate whether ghosting may occur (e.g.,whether it is possible for ghosting to occur). If any of the targetfrequency peaks is within one or more sets of frequency ranges whereghosting can occur, the LIDAR system may perform IQ processing, asdiscussed above. If the target is not within one or more sets of rangeswhere ghosting can occur, the LIDAR system may refrain from performingIQ processing (e.g., may not perform IQ processing) and perform realprocessing instead. For example, the LIDAR system may refrain from usingIQ circuit, modules, components, etc.

In one embodiment, the LIDAR system may vary, adjust, modify, etc., theset of frequency ranges where ghosting may occur based on the velocityof the LIDAR system. For example, the LIDAR system may increase/decreasethe boundaries of the set of frequency ranges where ghosting may occur,based on the speed/velocity (e.g., ego velocity) of the vehicle wherethe LIDAR system is located.

FIG. 6 is a block diagram of an example processing module 600 forselecting (e.g., determining, picking, calculating, etc.) peaksaccording to the present disclosure. The processing module 600 may bepart of a signal processing system of a LIDAR system. For example, theprocessing module 600 may be part of the signal processing system 303 ofthe LIDAR system 300, as illustrated in FIG. 3A and FIG. 4. In anotherexample, the processing module 600 may be part of signal processing unit112 illustrated in FIG. 1. In a further example, portions of theprocessing module 600 may be included in the time domain processor 402and the DFT process 404 of the signal processing system 303, asillustrated in FIG. 4. The processing module includes a mixing module601, a mixing module 602, a shifting module 611, ananalog-digital-converter (ADC) 621, an ADC 622, a mixing module 631, acombining module 641, and a FFT module 651. Each of the mixing module601, the mixing module 602, the shifting module 611, the ADC 621, theADC 622, the mixing module 631, the combining module 641, and the FFTmodule 651 may be hardware, software, firmware, or a combinationthereof.

As discussed above, the processing module 600 may receive a returnedsignal (e.g., target return signal 202 illustrated in FIG. 2) and mayprovide the returned signal to the mixing module 601 and the mixingmodule 602. The mixing module 601 may mix, shift, downshift, etc., thereturned signal by a transmit signal (which corresponds to the returnedsignal) to generate a downshifted signal 605. The downshifted signal 605may be provided to the ADC 621 which may generate an in-phase signal (I)based on the downshifted signal 605.

The shifting module 611 may shift the transmitted signal by 90 degreesand may provide the 90-degree shifted transmitted signal to the mixingmodule 602. The mixing module 602 may mix, shift, downshift, etc., thereturned signal by the 90-degree shifted transmitted signal to generatea downshifted signal 606. The downshifted signal 606 may be provided tothe ADC 622 which may generate a quadrature signal (Q) based on thedownshifted signal 606. The quadrature signal is provided to mixingmodule 631. The mixing module 631 also receives a complex or imaginarycomponent j. The mixing module 631 may mix the quadrature signal Q withthe imaginary component j to generate the signal j*Q.

The in-phase signal I and the signal j*Q are provided to the combiningmodule 641 which may combine the in-phase signal I and the signal j*Q togenerate a combined signal (I+(j*Q)). The combined signal I+(j*Q) isprovided to the FFT module 651 which may perform a FFT on the combinedsignal I+(j*Q) to generate a baseband signal.

As discussed above, the FFT of the combined signal I+(j*Q) may no longerbe symmetric because the combined signal I+(j*Q) is a complex signal.After the FFT of the combined signal, the magnitude/height of the imagepeaks may be reduced, suppressed, minimized, etc., when compared to themagnitude/height of the true peaks. This allows the LIDAR system toidentify the true peaks more easily, quickly, efficiently, etc.

Also as discussed above, the LIDAR system may determine if the frequencypeaks associated with the target are within one or more sets offrequency ranges where ghosting can occur. If the target is not withinone or more sets of ranges where ghosting can occur, the LIDAR systemmay refrain from performing IQ processing (e.g., may not perform IQprocessing). For example, the LIDAR system may power down or refrainfrom using the mixing module 602, the shifting module 611, the ADC 622,and the mixing module 631.

FIG. 7A is a signal magnitude-frequency diagram 700 illustratingfrequency ranges according to the present disclosure. A frequency of 0(e.g., 0 hertz, 0 terahertz, etc.) is illustrated in the signalmagnitude-frequency diagram 700. Frequency D_(MAX, DN) is alsoillustrated in the signal magnitude-frequency diagram 700. D_(MAX, DN)may be a maximum or threshold negative Doppler shift (e.g., a Dopplershift that occurs when an object is moving away from the LIDAR system)that the LIDAR system may be able to account for when detecting objects.Signal magnitude-frequency diagram 700 also refers to D_(MAX, UP).D_(MAX, UP) may be a maximum or threshold positive Doppler shift (e.g.,a Doppler shift that occurs when an object is moving towards from theLIDAR system) that the LIDAR system may be able to account for whendetecting objects. The Nyquist frequency F_(NYQUIST) is also illustratedin the signal magnitude-frequency diagram 700. In addition, thefrequency F_(NYQUIST)−D_(MAX, UP) is also illustrated in the signalmagnitude-frequency diagram 700.

The range of frequencies between 0 and D_(MAX, DN) may be a first rangeof frequencies where closer/close range ghosting may occur. The range offrequencies between F_(NYQUIST)−D_(MAX, UP) and F_(NYQUIST) may be asecond range of frequencies where far range ghosting may occur. Therange of frequencies between D_(MAX, DN) and F_(NYQUIST)−D_(MAX, UP) maybe a third range of frequencies where ghosting may not occur.

To determine whether close/closer range or far range ghosting couldoccur the LIDAR may analyze the peaks that are detected. In someembodiments, if a positive peak of a first chirp/sweep is less thanD_(MAX, DN), and the positive peak of a second chirp/sweep is less than2*D_(MAX, DN), close range ghosting mitigation may be applied. In otherembodiments, if the positive peak of either the first chirp/sweep isgreater than F_(NYQUIST)−D_(MAX, UP), and the positive peak of thesecond chirp/sweep is greater than (F_(NYQUIST)−(2*D_(MAX, UP))), farrange ghosting mitigation may be applied. In further embodiments, ifboth positive peaks are in the range (D_(MAX, DN),F_(NYQUIST)−D_(MAX, UP), no ghosting mitigation (e.g., no IQ processing)may need to be applied.

In some embodiments, instead of detecting peaks to determine whethercloser or far range ghost mitigation should be used, the LIDAR may useenergy detection. For example, peak detection may use more computationalresources (e.g., processing resources, processing capacity, processingpower) and/or memory. Peak detection may also take more time to perform.Detecting the total amount of energy (e.g., energy detection) within arange of frequencies, rather than detecting peaks may allow the LIDAR todetermine which type of ghost mitigation should be used more quicklyand/or efficiently.

FIG. 7B is a signal magnitude-frequency diagram 750 illustratingfrequency ranges according to the present disclosure. A frequency of 0(e.g., 0 hertz, 0 terahertz, etc.) is illustrated in the signalmagnitude-frequency diagram 700. Frequencies −F_(NYQUIST),−F_(NYQUIST)+D_(MAX, UP), −D_(MAX, DN), and F_(NYQUIST) are alsoillustrated in the signal magnitude-frequency diagram 750. D_(MAX) maybe a maximum or threshold Doppler shift (e.g., a Doppler shift thatoccurs when an object is moving away from the LIDAR system) that theLIDAR system may be able to account for when detecting objects.

As discussed above, a combined signal may be determined (e.g.,generated, computed, constructed, etc.) as I−(j*Q) for up-chirps andI+(j*Q) for down-chirps to reduce the range or amount of frequenciesthat are processed by the LIDAR system. This may cause all of the truepeaks to be at positive frequencies in the absence of Doppler shift.When the true peaks are at the positive frequencies, the LIDAR systemmay scan for peaks at the positive frequencies only (e.g., may not scanfor peaks at negative frequencies). Alternatively, the combined signalmay be determined as I+(j*Q) for up-chirps and I−(j*Q) for down-chirps.This may cause all of the true peaks to be at negative frequencies. Whenthe true peaks are at the negative frequencies, the LIDAR system mayscan for peaks at the negative frequencies only (e.g., may not scan forpeaks at positive frequencies).

In the case where the true peaks are forced to be at positivefrequencies in the absence of Doppler shift, the presence of Dopplershift may cause the peaks to move to negative frequencies. If closerange ghosting is occurring, the true peak may be in the range offrequencies between −D_(MAX, DN) and 0. The LIDAR system may scan fortrue peaks in the range of frequencies between −D_(MAX, DN) and 0. Iffar range ghosting is occurring, a true peak may be in the range offrequencies between F_(NYQUIST) and (F_(NYQUIST)+D_(MAX)). which willget aliased into the range −F_(NYQUIST) to (−F_(NYQUIST)+D_(MAX, UP)).The LIDAR system may scan for true peaks in the range of frequenciesbetween −F_(NYQUIST) and −F_(NYQUIST)+D_(MAX, UP). True peaks cannot belocated between the frequencies −(F_(NYQUIST)−D_(MAX, UP)) and−D_(MAX, DN). The LIDAR system may not scan the range of frequenciesbetween −(F_(NYQUIST)−D_(MAX, UP)) and −D_(MAX, DN). By analyzingcertain ranges of frequencies (e.g., between F_(NYQUIST) and(F_(NYQUIST)+D_(MAX, UP))) and refraining from analyzing other ranges offrequencies (e.g., between (F_(NYQUIST)+D_(MAX, UP)) and −D_(MAX, DN)),the LIDAR system identify true peaks more quickly and/or efficiently(e.g., using less energy or processing power). In the case where thetrue peaks are forced to be at negative frequencies in the absence ofDoppler shift, the presence of Doppler shift could still move peaks topositive frequencies.

FIG. 8 is a flowchart illustrating a method 800 in a LIDAR system, suchas LIDAR system 100 or LIDAR system 300, for selecting peaks accordingto the present disclosure. Method 800 may be performed by processinglogic that may comprise hardware (e.g., circuitry, dedicated logic,programmable logic, a processor, a processing device, a centralprocessing unit (CPU), a system-on-chip (SoC), etc.), software (e.g.,instructions running/executing on a processing device), firmware (e.g.,microcode), or a combination thereof. In some embodiments, the method800 may be performed by a signal processing system of a LIDAR system(e.g., the signal processing system 303 of the LIDAR system 300, asillustrated in FIG. 3A and FIG. 4).

The method 800 begins at operation 805 where the processing logictransmits one or more optical beams comprising an up-chirp frequencymodulation and a down-chirp frequency modulation toward a target in afield of view of a light detection and ranging (LIDAR) system.Optionally, the processing logic may introduce phase modulations intothe one or more optical beams. At operation 810, the processing logicreceives one or more returned signals of the up-chirp and the down-chirpas reflected from the target.

The processing logic may determine whether target peaks are within oneor more ghosting ranges (e.g., is within a distance where either farrange ghosting or close range ghosting may occur) at block 815. If thetarget is not within one or more ghosting ranges, the processing logicmay determine the target location based on a baseband signal atoperation 825, as discussed above in FIG. 5. The processing logic mayalso optionally set, determine, adjust, vary, etc., the ghosting rangesbased on the velocity of the LIDAR system at operation 815.

If the target is within one or more ghosting ranges, the processinglogic may perform IQ processing at block 820, as discussed above in FIG.5. For example, the processing logic may generate in-phase andquadrature signals, may combine the quadrature signal with an imaginaryunit (e.g., j), may perform a FFT on the combined signal, etc. The IQprocessing may decrease, suppress, etc., the magnitude/height of theimage peaks in the baseband signal. At block 825, the processing logicmay determine the target location based on the peaks with the highestmagnitude/height (e.g., the true peaks) in the baseband signal.

The preceding description sets forth numerous specific details such asexamples of specific systems, components, methods, and so forth, inorder to provide a thorough understanding of several examples in thepresent disclosure. It will be apparent to one skilled in the art,however, that at least some examples of the present disclosure may bepracticed without these specific details. In other instances, well-knowncomponents or methods are not described in detail or are presented insimple block diagram form in order to avoid unnecessarily obscuring thepresent disclosure. Thus, the specific details set forth are merelyexemplary. Particular examples may vary from these exemplary details andstill be contemplated to be within the scope of the present disclosure.

Any reference throughout this specification to “one example” or “anexample” means that a particular feature, structure, or characteristicdescribed in connection with the examples are included in at least oneexample. Therefore, the appearances of the phrase “in one example” or“in an example” in various places throughout this specification are notnecessarily all referring to the same example.

Although the operations of the methods herein are shown and described ina particular order, the order of the operations of each method may bealtered so that certain operations may be performed in an inverse orderor so that certain operations may be performed, at least in part,concurrently with other operations. Instructions or sub-operations ofdistinct operations may be performed in an intermittent or alternatingmanner.

The above description of illustrated implementations of the invention,including what is described in the Abstract, is not intended to beexhaustive or to limit the invention to the precise forms disclosed.While specific implementations of, and examples for, the invention aredescribed herein for illustrative purposes, various equivalentmodifications are possible within the scope of the invention, as thoseskilled in the relevant art will recognize. The words “example” or“exemplary” are used herein to mean serving as an example, instance, orillustration. Any aspect or design described herein as “example” or“exemplary” is not necessarily to be construed as preferred oradvantageous over other aspects or designs. Rather, use of the words“example” or “exemplary” is intended to present concepts in a concretefashion. As used in this application, the term “or” is intended to meanan inclusive “or” rather than an exclusive “or”. That is, unlessspecified otherwise, or clear from context, “X includes A or B” isintended to mean any of the natural inclusive permutations. That is, ifX includes A; X includes B; or X includes both A and B, then “X includesA or B” is satisfied under any of the foregoing instances. In addition,the articles “a” and “an” as used in this application and the appendedclaims should generally be construed to mean “one or more” unlessspecified otherwise or clear from context to be directed to a singularform. Furthermore, the terms “first,” “second,” “third,” “fourth,” etc.as used herein are meant as labels to distinguish among differentelements and may not necessarily have an ordinal meaning according totheir numerical designation.

What is claimed is:
 1. A method, comprising: transmitting, toward atarget in a field of view of a light detection and ranging (LIDAR)system, one or more optical beams comprising at least one up-chirpfrequency and at least one down-chirp frequency; receiving, from thetarget, a set of returned signals based on the one or more opticalbeams; determining whether peaks associated with the target are withinone or more sets of frequency ranges comprising signal attribute valuescorresponding to a lower likelihood of accurately calculating a locationor speed of the target; provided the peaks associated with the targetare within the one or more sets of frequency ranges, performing in-phasequadrature phase (IQ) processing on the one or more received signalswherein the IQ processing reduces one or more magnitudes of one or morepeaks of the peaks associated with the target; and determining one ormore of the target location, a target velocity, and a targetreflectivity using the peaks associated with the target.
 2. The methodof claim 1, wherein: the peaks associated with the target comprise afirst set of peaks and a second set of peaks; the first set of peakscomprises a first true peak and a first image peak; the second set ofpeaks comprises a second true peak and a second image peak; and the IQprocessing reduces a first magnitude of the first image peak and asecond magnitude of the second image peak.
 3. The method of claim 2,wherein determining the target location using the first set of peaks andthe second set of peaks comprises: selecting the first true peak fromthe first set of peaks and the second true peak from the second set ofpeaks; and determining the target location based on the first true peakand the second true peak.
 4. The method of claim 1, wherein the one ormore sets of frequency ranges are based on an ego-velocity of the LIDARsystem.
 5. The method of claim 1, wherein performing IQ processingcomprises: generating a first signal and second signal based on the setof returned signals, wherein the first signal is shifted 90 degrees fromthe second signal; generating a third signal, wherein the third signalcomprises a combination of the first signal and an imaginary unit; andcombining the third and the second signal to generate a combined signal.6. The method of claim 5, wherein performing IQ processing furthercomprises: applying a fast Fourier transformer to the combined signal.7. The method of claim 5, wherein combining the third and the secondsignal comprises: subtracting the third signal from the second signalfor an up-chirp and adding the third signal to the second signal for adown-chirp; or adding the third signal to the second signal for anup-chirp and subtracting the third signal from the second signal for adown-chirp.
 8. The method of claim 7, wherein subtracting the thirdsignal from the second signal for an up-chirp and adding the thirdsignal to the second signal for a down-chirp reduces a range offrequencies that is processed to determine one or more of the targetlocation, the target velocity, and the target reflectivity.
 9. Themethod of claim 1, further comprising: provided the peaks associatedwith the target are not within the one or more sets of frequency ranges,refraining from using in-phase quadrature phase (IQ) circuitry.
 10. Alight detection and ranging (LIDAR) system, comprising: an opticalscanner to transmit one or more optical beams comprising at least oneup-chirp frequency and at least one down-chirp frequency toward atargets in a field of view of the LIDAR system and receive a set ofreturned signals based on the one or more optical beams; an opticalprocessing system coupled to the optical scanner to generate a basebandsignal in a time domain from the return signal, the baseband signalcomprising frequencies corresponding to LIDAR target ranges; and asignal processing system coupled to the optical processing system,comprising: a processing device; and a memory to store instructionsthat, when executed by the processing device, cause the LIDAR system to:determine whether peaks associated with the target are within one ormore sets of frequency ranges comprising signal attribute valuescorresponding to a lower likelihood of accurately calculating a locationor speed of the target; provided the peaks associated with the targetare within the one or more sets of frequency ranges, perform in-phasequadrature phase (IQ) processing on the one or more received signalswherein the IQ processing reduces one or more magnitudes of one or morepeaks of the peaks associated with the target; and determine one or moreof the target location, a target velocity, and a target reflectivityusing the peaks associated with the target.
 11. The LIDAR system ofclaim 10, wherein: the peaks associated with the target comprise a firstset of peaks and a second set of peaks; the first set of peaks comprisesa first true peak and a first image peak; the second set of peakscomprises a second true peak and a second image peak; and the IQprocessing reduces a first magnitude of the first image peak and asecond magnitude of the second image peak.
 12. The LIDAR system of claim11, wherein to determine the target location using the first set ofpeaks and the second set of peaks the LIDAR system is further to: selectthe first true peak from the first set of peaks and the second true peakfrom the second set of peaks; and determine the target location based onthe first true peak and the second true peak.
 13. The LIDAR system ofclaim 10, wherein the one or more sets of frequency ranges are variablebased on an ego-velocity of the LIDAR system.
 14. The LIDAR system ofclaim 10, wherein to perform IQ processing the LIDAR system is furtherto: generate first signal and a second signal based on the set ofreturned signals, wherein the first signal is shifted 90 degrees fromthe second signal; generate a third signal, wherein the third signalcomprises a combination of the first signal and an imaginary unit; andcombine the third and the second signal to generate a combined signal.15. The LIDAR system of claim 14, wherein to perform IQ processing theLIDAR system is further to: apply a fast Fourier transformer to thecombined signal.
 16. The LIDAR system of claim 14, wherein to combinethe third signal and the second signal the LIDAR system is further to:subtract the third signal from the second signal for an up-chirp and addthe j third signal to the second signal for a down-chirp; or add thethird signal to the second signal for an up-chirp and subtract the thirdsignal from the second signal for a down-chirp.
 17. The LIDAR system ofclaim 16, wherein subtracting the third signal from the second signalfor an up-chirp and adding the third signal to the second signal for adown-chirp reduces a range of frequencies that is processed to determineone or more of the target location, the target velocity, and the targetreflectivity.
 18. The LIDAR system of claim 10, wherein the LIDAR systemis further to: provided the peaks associated with the target are notwithin the one or more sets of frequency ranges, refrain from usingin-phase quadrature phase (IQ) circuitry.
 19. A light detection andranging (LIDAR) system, the system comprising: a processor; and a memoryto store instructions that, when executed by the processor, cause theLIDAR system to: transmit, toward a target in a field of view of theLIDAR system, one or more optical beams comprising at least one up-chirpfrequency and at least one down-chirp frequency; receive, from thetarget, a set of returned signals based on the one or more opticalbeams; determine whether peaks associated with the target are within oneor more sets of frequency ranges comprising signal attribute valuescorresponding to a lower likelihood of accurately calculating a locationor speed of the target; provided the peaks associated with the targetare within the one or more sets of frequency ranges, perform in-phasequadrature phase (IQ) processing on the one or more received signalswherein the IQ processing reduces one or more magnitudes of one or morepeaks of the peaks associated with the target; and determine one or moreof the target location, a target velocity, and a target reflectivityusing the peaks associated with the target.
 20. The LIDAR system ofclaim 19, wherein: the peaks associated with the target comprise a firstset of peaks and a second set of peaks; the first set of peaks comprisesa first true peak and a first image peak; the second set of peakscomprises a second true peak and a second image peak; and the IQprocessing reduces a first magnitude of the first image peak and asecond magnitude of the second image peak.